Field of the Invention
The present invention relates to addition compounds, to processes for preparing these addition compounds, and to uses of these addition compounds as dispersants or anti-sedimentation agents, particularly for pigments, fillers and matting agents.
Discussion of the Background
In coatings, solid particles present in formulations normally include pigments used for colouring, extenders used as fillers and/or other solid materials for special purposes like matting agents. A dispersant is a substance which facilitates the dispersing and stabilizing of these solid particles in a liquid medium by lowering the interfacial tension between these two components. The dispersants are normally surface-active substances of anionic, cationic or nonionic structure. The presence of dispersants substantially reduces the dispersing energy required and minimizes the dispersing time as well. The dispersants, in relatively small quantities, are either applied directly to the solid particles or added to the liquid medium. The amount of dispersant applied is dependent on the size and nature of the surface of the solid particles that are to be dispersed. Carbon black, for example, requires larger amounts of dispersant than titanium dioxide needs so as to obtain a particle size as small as possible which may usually be in the nanometer range. However, for matting agents such as silica which has a generally high density, it is challenging to disperse and stabilize it.
There have been many efforts aimed at providing effective dispersants for various solid particles, especially for pigments, fillers and matting agents that allow for coating compositions which are stable to re-agglomeration and sedimentation. A common problem with matting agents in particular, is the sedimentation of the heavy and comparatively large particles that are needed to obtain the matting effect in the paint formulation as well as in the form of concentrates. A further complication in these sediments can be the formation of hard sediments that, in contrast to soft sediments, cannot be redispersed by shaking or stirring, but require strong shear forces to be broken up, such as the employment of a grinding, milling or dispersing step.
For example, polymeric dispersants based on polyfunctional isocyanates, polymeric compounds and compounds bearing dispersing groups have been known for a long time, and for example been described in U.S. Pat. No. 4,647,647, U.S. Pat. No. 5,425,900, U.S. Pat. No. 6,506,899, U.S. Pat. No. 7,741,404, U.S. Pat. No. 8,362,300 etc.
U.S. Pat. No. 4,647,647 discloses dispersants made by reacting polyisocyanate having an average functionality of 2.5-6 with monohydroxyl polyether and/or polyester compounds, and isocyanate reactive compounds having at least one tertiary amino group or one basic ring nitrogen carrying no hydrogen atom.
U.S. Pat. No. 6,506,899 discloses polymeric pigment dispersants prepared by reacting an isocyanate with a hydrophilic poly(ether glycol)alkyl ether, a hydrophobic polyester or polyacrylate, and a diamine which contains a primary amine and a tertiary amine.
U.S. Pat. No. 7,741,404 describes a non-aqueous composition containing a solid particulate matter, an organic medium and a polyurethane dispersant having an essentially linear backbone and laterally attached solvent-solubilizing side chains of a polyester, a polyether, a polyacrylate or a polyolefin including mixtures of such side chains.
U.S. Pat. No. 8,362,300 describes addition compounds from the reaction of a) one or more polyisocyanates containing uretdione groups with b) one or more compounds of the formula Y—(XH)n and followed by the reaction with c) one or more compounds of the general formula Z—NHR. In the formulation, XH is a isocyanate reactive group, Y is a monomeric or polymeric group comprising one or more aliphatic, cycloaliphatic, araliphatic and/or aromatic groups that is not isocyanate reactive, n is 1, 2 or 3, R is hydrogen or a alkyl group and Z is an aliphatic, cycloaliphatic and/or aromatic basic radical.
The background art products contain so-called anchor groups which absorb onto the solid particle to be dispersed and also have a polymer chain which is compatible with the dispersion medium. There are large numbers of polyurethane dispersants commercially available. However, they offer only partial solutions to the problems encountered.
In some dispersant preparations, side reactions may occur and the resultant products are highly complex and poorly defined reaction mixtures that may be difficult to reproduce resulting in inconsistent performances. There are other problems as well, for example, some of these dispersant preparations need to be conducted under extreme reaction conditions such as very high temperatures and long reaction times. This increases the production costs and results in limited usage of the final coating. Therefore, there is a growing need for dispersants for solid particles which exhibit improved properties compared with those available in the background art and that can be produced more efficiently.